it doesnt need to but it's better thats why scrubbies,ceramic rings etc has a more roughed/more surface are which = to more BBA that can work just not as well.
I agree. I think you need a more porous surface. Even if the beads did work, I don't think they'd support as large a bacterial colony as a more porous media.
They would function, but a more porous surface is generally the route to go. Then again, I have never seen a formula for required surface area per fish that had anything more than a lot of guess work involved.